Etiol.^oy. 



703 



and especially in breeds of doi>-s in wliicli the spinal colnnin is 

 too long in comparison with the length of the animal's legs. 

 This was shown by Jakob regarding the striking disproportion- 

 ate length of the body and the limbs in the case of dachshunds. 

 The prejudicial effect of this body-formation is increased by the 

 weakness of the joints of the limbs. A few observations have 

 shown that the joints that are affected most commonly are the 

 tenth and thirteenth dorsal, the first and fourth lumbar, and 

 somewhat more rarely the second and fourth cervical. It is 

 very rarely that other joints are 

 affected. According to Pexler the 

 cervical vertebraB are involved as 

 frequently as the dorsal and lumbar 

 joints, and Cadeac believes that the 

 disease occurs principally in the 

 cervical vertebra?. It is rare that a 

 single joint is affected. In cases in 

 which the posterior dorsal vertebra^ 

 are involved the lumbar bones are 

 also affected, and, similarly, disease 

 in the cervical vertebrae is associ- 

 ated with disease in the dorsal bones. 

 The disease is not, as a rule, co-ex- 

 tensive in all the joints. 



Dexler's histological investigations have 

 shown that the disease begins with the for- 

 mation of a cellular tissue richly supplied 

 with vessels in the periosteum of the verte- 

 bra and the intervertebral di^cs, the tissue in 

 the latter ease containing islands of hyaline 

 cartilage. Later the number of vessels de- 

 creases, the connective tissue shrinks, and the 

 islands of cartilage increase in size and final- 

 ly become calcified. 



Fig. 09. Projection of the inter- 

 vertebral discs into the spinal 

 canal owing to encliondrosis inter- 

 vertebralis. (a) Between the sec- 

 ond and third cervical, and (b) 

 between the eleventh and twelfth 

 dorsal vertebme. At (a) the dura 

 was adherent to the prominence. 



At the postmortem there are 

 found, both in the vertebral canal 

 and also on the outer surfaces of the 

 vertebrae, white prominences which 

 at first are soft, but afterwards be- 

 come bony. In the later stages the bony grow^ths within the 

 canal, which are boatlike in shape, extend from one vertebra to 

 the next and form a connection between the two. As a result of 

 persistent irritation, in cases that have been in existence for 

 some time a chronic inflammation of the dura is set up in the 

 immediate neighborhood. This generally leads to the production 

 of new cartilaginous tissue which calcifies subsequently. In 

 time the thickened portions of the membrane become joined to 

 the intervertebral growths and so further reduce the lumen of 

 the canal (fig. 99). 



Whether the process described in the intervertebral discs is actually inflam- 

 matory or of some other nature is not definitely known, but the inflammatory nature 



